A crankshaft of an internal combustion engine is rotatably supported in its journal part by a lower portion of a cylinder block of the engine via a main bearing constituted by a pair of half bearings combined into a cylindrical shape. One or both of the pair of half bearings are combined with a half thrust bearing for receiving an axial force of the crankshaft. The half thrust bearing is placed on one or both end faces in an axial direction of the half bearing.
The half thrust bearing receives an axial force generated in an axial direction of the crankshaft. That is, the half thrust bearing is provided for the purpose of bearing an axial force applied to the crankshaft, for example, when the crankshaft is connected to a transmission by a clutch.
The crankshaft of the internal combustion engine is supported in its journal part by the lower portion of the cylinder block of the engine via the main bearing constituted by the pair of half bearings. Lubrication oil is fed from an oil gallery in a cylinder block wall, via a through hole in a wall of the main bearing, into a lubrication oil groove formed along an inner surface of the main bearing. Thus, the lubrication oil is supplied into the lubrication oil groove of the main bearing and is then supplied to the half thrust bearing.
In recent years, an oil pump for supplying lubrication oil has been downsized in order to improve fuel economy of the internal combustion engine, and this causes a reduction in an amount of lubrication oil supplied to the bearings. Accordingly, an amount of lubrication oil leaked from end faces of the main bearing decreases, and thus an amount of lubrication oil supplied to the half thrust bearing also tends to decrease. As a measure to address this problem, for example, it has been proposed to improve retainability of lubrication oil by forming thin grooves in parallel to each other on a sliding surface of the half thrust bearing (see JP 2001-323928A, for example) or by forming a plurality of minute recesses on a sliding surface of the half thrust bearing (see JP 2000-504089A, for example).
In recent years, due to the reduction in the amount of lubrication oil supplied to the half thrust bearing as described above, a surface of a thrust collar of the crankshaft directly comes into contact with a sliding surface of the half thrust bearing during operation of the internal combustion engine, and thus friction loss is more likely to occur. Furthermore, in recent years, a shaft diameter of the crankshaft is reduced in order to reduce a weight of the internal combustion engine, and this causes the crankshaft to have lower rigidity than a conventional crankshaft. Thus, during operation of the internal combustion engine, deflection is more likely to occur in the crankshaft, and this tends to cause the crankshaft to vibrate greatly. Accordingly, the surface of the thrust collar is more likely to directly come into contact with a portion of the sliding surface near a circumferential center portion of the half thrust bearing. Thus, damage such as seizure is more likely to occur.
In order to address the situation, JP 2001-323928A and JP 2000-504089A each disclose a configuration for improving retainability of lubrication oil on the sliding surface by forming oil grooves along a circumferential direction on the sliding surface (JP 2001-323928A) and by forming a plurality of minute recesses on the sliding surface (JP 2000-504089A).
However, even if the technique of JP 2001-323928A or JP 2000-504089A is employed, in a case where the deflection of the crankshaft causes the crankshaft to vibrate greatly, it is difficult to prevent seizure when the thrust collar of the crankshaft comes into contact with a portion of the sliding surface near an outer edge or an inner edge in a radial direction, in particular, near the circumferential center portion of the half thrust bearing.
An object of the present invention is to provide a half thrust bearing of a crankshaft of an internal combustion engine, that can suppress seizure during operation of the internal combustion engine.
In an aspect of the present invention, a half thrust bearing is provided for receiving an axial force of a crankshaft of an internal combustion engine. The half thrust bearing has a semi-annular shape, and has a sliding surface for receiving the axial force and a back surface opposite to the sliding surface. The sliding surface includes a plurality of recesses. Each recess has a recess surface recessed from the sliding surface toward the back surface of the half thrust bearing. The recess surface is convex toward the back surface in a cross-sectional view in a direction along a center line of the half thrust bearing. The recess surface includes a plurality of grooves along a center line. The grooves are recessed from the recess surface toward the back surface of the half thrust bearing. The grooves extend along the center line direction V of the half thrust bearing so that smooth surfaces and the grooves are alternately arranged on the recess surface in a horizontal direction H of the half thrust bearing.
Here, the “horizontal direction (H)” of the half thrust bearing indicates a direction connecting center points of both end faces of the half thrust bearing. The “center line direction (V)” (or vertical direction) of the half thrust bearing indicates a direction parallel to the sliding surface and perpendicular to the horizontal direction (H).
According to an embodiment of the present invention, the recesses preferably have a depth of 2 to 50 μm.
According to an embodiment of the present invention, the grooves preferably have a depth of 0.2 to 3 μm. Furthermore, the grooves preferably have a width of 5 to 50 μm. Furthermore, the grooves are preferably arranged with a pitch of 5 to 100 μm.
According to an embodiment of the present invention, the recesses preferably have an opening of a circular shape, an elliptical shape, or a quadrilateral shape. More preferably, the opening has an elliptical shape with a major axis of the elliptical shape extending along the center line direction of the half thrust bearing.
According to an embodiment of the present invention, the recess surface is preferably convex toward the back surface of the half thrust bearing in a cross-sectional view along the horizontal direction of the half thrust bearing.
According to an embodiment of the present invention, the recesses are preferably uniformly located throughout the sliding surface of the half thrust bearing.